According to Lazarus Long love is what happens when you're not having sex.
Having now read Time Enough for Love, apparently "love" primarily consists of
talking about sex, and making-out with teenage girls.

Heinlein for all his brilliance as a writer was also a dirty old man, and sadly
that completely ruins this book. The central conceit, two-thousand-year old man
contemplating finally ending it all settles down to tell some tall tales to one
of his distant descendants, is quite interesting, and a couple of the individual
tales (rescuing the twins, and the wagon-train) manage to be pretty good until
they essentially stop being about anything other than sex.

It's not that there's sex in the story, or even taboo sex, but that Heinlein
let's the story cease to be about anything other than taboo sex. Both the
stories-within-a-story work despite having taboo sexual themes, because there's
more to them than that, but essentially all the other stories are just sex,
perverted sex, and talking about sex.